From OMNeT++ Wiki

Main: Using OMNeT++ 3.x with MinGW

NOTE: These instructions refer to the older 3.x versions of OMNeT++. 4.x releases already contain MinGW and the necessary libraries.

Installation instructions in a nutshell

You need to compile OMNeT++ from source, as the libs in the Windows binary version are for Visual C++ and they are not compatible with MinGW. The procedure is essentially the same as on Linux, except that the compilation environment has to be set up first.

1. Install required software: MSYS and MinGW; Windows ports of bison and flex (UnxUtils versions are fine); Tcl/Tk; BLT; Perl. LibXML/LibXSLT or at least Expat is also recommended. Optional libraries: Akaroa, MPI.
2. Make sure bison, flex, and Tcl/Tk are in the PATH, and the following variables are set correctly: BISON_SIMPLE, TCL_LIBRARY.
3. Download OMNeT++ source package and unpack it (say into c:\omnetpp).
4. Add c:\omnetpp\bin your PATH.
5. Edit c:\omnetpp\configure.user according to your system. Use Windows-style path names with *forward* slashes (/). If a directory name contains space, use the short name (like C:/PROGRA~1).
6. Then fire up the MSYS shell and type the usual GNU stuff: ./configure, make. If make goes through, you've made it!
7. Try that the sample simulations, gned, nedtool and opp_makemake work.

If you are unsure or have run into trouble, please read the detailed instructions.

MinGW issues

Problem with gcc 3.4.4 (cygming special)

OMNeT++ 3.2 does not compile with this version of gcc. gcc --version displays the version number of your gcc.

As there is no problem with several other gcc versions (gcc-4.0.1 , gcc-3.4.0 , gcc-3.3.5 on Linux, gcc-3.3.3 (cygwin special), gcc-3.2.3 (mingw special), gcc-3.3.3 (linux ia64)) and with C++ compilers from other vendors (the Intel compiler, Visual C++), this can be safely considered a compiler bug. Please install another version of gcc.

BLT for MinGW

TBD